The idea of this tool came to us out of pure necessity. In the twenty odd years of framing, I have always run into the same problem when cutting plywood at angles. The problem was making an accurate angle line mark without the help of either a nail or another person. I have tried many methods, but was not pleased with the results and came to the conclusion that I had to invent something to solve that problem. Other ways of marking plywood would be a straight edge, but more often than not, the straight edge would either be too long or too short. If it was too long when the line was marked, the straight edge would move or plywood would move. If it was too short, well, it just wouldn't reach from one end to the other. I tried clamping the line to the plywood. Since I would have to roll the line on the plywood, it created other problems: (a) it would not be accurate. (b) it would slip off the clamp. A nail would split the material and it too, was inaccurate and cause the line to have a tendency to run down the edge of the plywood on steeper angles.